Not everything can be shipped through the United States Postal Service (USPS). These include items that are illegal or can cause harm to postal employees or damage postal equipment as well as the mails of other customers. Some restricted items can be mailed but only in limited quantities with special packaging. Some also require licenses and permits. Mailing restricted items is considered a crime and is punishable by fine, imprisonment, and/or another penalty. Here is a list of items that are not mailable through the USPS.
Any item that can be dangerous or injurious to life, health, or property, otherwise known as hazardous matter, is non-mailable. Hazardous materials include explosives, gases, flammable liquids, toxic/infectious substances, radioactive materials, corrosive substances, etc.
Restricted matter includes articles on which mailing restrictions have been imposed for reasons other than the risk of harm to persons or property involved in moving the mail. Only licensed individuals are permitted to ship these items. Restricted matter includes intoxicating liquors, firearms, sharp instruments, odor-producing materials, motor vehicle master keys, locksmithing devices, controlled substances/drugs, animal fighting ventures which include live animals used for animal fighting, animal fighting accessories, and other animal fighting matter such as publications promoting an animal-fighting venture.
The perishable matter is anything that can deteriorate in the mail and thereby lose value, create a health hazard, or cause an obnoxious odor, nuisance, or disturbance, under ordinary mailing conditions. There is perishable matter that can be sent at the mailer’s own risk as long as it is packaged as required and when it can be delivered within appropriate and reasonable time limits to prevent deterioration. Mailable perishable matter includes live healthy animals (except poisonous insects and pests), properly packed food items, and plants that are not listed as endangered or illegal.
Other Restricted Matter includes fraudulent information and pornographic materials or any other printed items that are sexually graphic.